The invention relates generally to damping vibrations in dynamically loaded metal components. More specifically, the invention relates to utilizing Shape Memory Alloys (SMAs) for damping vibrations in rotating components and system lines, thereby reducing fatigue failures.
Dynamically loaded parts, such as high energy rotating components of turbine engines and pumps, can be subject to highly damaging vibrational forces during operation. During the design stage, a rough estimate of the vibrational modes is made and the operational RPM is designed to avoid the resonance of the predicted vibrational modes. In addition, blade tip dampers, frictional dampers and damper seals are routinely incorporated to further reduce the potential of detrimental vibrations. Sometimes redesign of rotation components are required due to component failures encountered during the development phase. In addition, the success of the redesign hinges on the understanding of the newly uncovered vibrational modes through failure analysis.
Superelastic alloys, or shape memory alloys (SMA), have the unique ability to be repeatedly deformed to high strain levels and still return to their original shape each time a load is applied without accumulating classic fatigue damage. This unique behavior is attributed to a strain-induced martensitic transformation in the near martensite crystal structure. In the fully martensitic state, the alloy deforms by a twinning mechanism changing crystallographic variants of the martensites. A hysteresis loop forms as the load is reversed. A high degree of mechanical energy dissipation, or internal damping, is associated with the fully reversible martensitic phase transformation, or twinning, that is characteristic of superelastic alloys. This damping mechanism is called hysteresis damping and is independent of vibrational frequency. High internal damping is beneficial in preventing premature fatigue failures in components subjected to large vibrating forces, which are often encountered in gas turbines, pumps and compressors.
Many propulsion components, e.g. turbine blades and disks, are subject to high vibration levels that can cause serious fatigue damage. Current solutions to protect against fatigue damage involve frictional damping, geometric attachments to reduce vibrational amplitudes for predicted vibrational modes, and use of frictional damper seals and inserts. The frictional damping may fail due to sticking of the frictional interface, and geometrical changes may not be possible due to the design being constrained by the specific strength and density of the component material. Additional drawbacks of current solutions include frequency dependent damping that requires precise knowledge of the vibrational modes of the component and drilling holes in the component for mechanical attachment resulting in an extra parts count.
It would therefore be desirable to employ the use of superelastic alloys in the construction of dynamically loaded parts, such as rotating components and system lines, to reduce vibrational amplitudes and eliminate premature fatigue failures.
In a preferred form, the present invention is directed to a method for damping vibrations in a turbine. The method includes performing structural dynamics analysis on the turbine to determine at least one area of high vibratory stress on the turbine, and performing thermal analysis of the turbine to determine at least an approximate maximum operating temperature at the area of high vibratory stress. Additionally, the method includes utilizing hysteresis damping by selecting a shape memory alloy (SMA) having a martensitic-to-austenite transformation temperature substantially similar to the approximate maximum operating temperature at the area of high vibratory stress and disposing the selected SMA on the turbine at the related area of high vibratory stress.
In another preferred form, the present invention is directed to a turbine engine that is resistant to vibratory damage during operation. The engine includes a housing and a disk and blade assembly rotatable within the housing, wherein the disk and blade assembly has at least one area susceptible to high vibratory stress during operation of the engine. The engine further includes a shape memory alloy (SMA) disposed on the disk and blade assembly at the area of high vibratory stress. The SMA is adapted to dissipate vibrational energy in the blade and/or disk as a result of hysteresis loops generated by the SMA.